Capturing static and dynamic correlations by a combination of projected Hartree-Fock and density functional theories

Author

Garza, Alejandro J.; Jiménez-Hoyos, Carlos A.; Scuseria, Gustavo E.

Date

2013

Abstract

This paper explores the possibility of combining projected Hartree-Fock and density functional theories
for treating static and dynamic correlations in molecular systems with mean-field computational
cost. The combination of spin-projected unrestricted Hartree-Fock (SUHF) with the TPSS correlation
functional (SUHF+TPSS) yields excellent results for non-metallic molecular dissociations and
singlet-triplet splittings. However, SUHF+TPSS fails to provide the qualitatively correct dissociation
curve for the notoriously difficult case of the chromium dimer. By tuning the TPSS correlation parameters
and adding complex conjugation symmetry breaking and restoration to SUHF, the right curve
shape for Cr2 can be obtained; unfortunately, such a combination is found to lead to overcorrelation
in the general case.